Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 261906 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 306 PM EDT MON SEP 26 2016 .SYNOPSIS...
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A cold front will approach from the west tonight and then move very slowly southeast across central NC through Wednesday.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 250 PM Monday Slow erosion of stratus continue across the heart of the Piedmont, with destablization in the Foothills and western Piedmont owing to higher dewpoints/theta e across the periphery of the retreating high off the New England coast. Scattered convection out ahead of the synoptic front, which stretches from Memphis to Pittsburgh, will drift east toward the western Piedmont through this evening, though with time the deep layer flow will back to more southwesterly and the entire system will slow. Thus, highest POPs (50-60%) will be over the western Piedmont tonight, with 20% or less east of US-1. Most Cams show the front hanging up over the northwest Piedmont, with a couple rounds of showers overnight, which could lead to some localized minor flooding, particularly given an area of 2+ inch PW off the SC coast they should be tapped by southeasterly flow this evening. However, there isn`t enough support from guidance to raise flags about any significant flooding threat. Lows 66-69.
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&& .SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/...
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As of 250 PM Monday... The cold front will inch eastward into the Piedmont on Tuesday, slowed further by system parallel flow induced by the upper low that will close off and dig toward the Tenn Valley. PW will remain relatively high at 1.75", though the source of higher PW off the coast looks to be cut off by a surface wave that lights northeast along the NC coast. Forcing is pretty much limited to moisture convergence along the front, with better height falls later Tuesday night ahead of the aforementioned upper low. Despite weak lapse rates aloft, highs in the upper 70s/lower 80s should result in weak instability and trigger scattered to numerous showers and a few isolated, mainly in the Piedmont. Increasing mid-level wind fields will increase the shear over the region Tuesday afternoon, but weak instability (better Wednesday) will ultimately limit the threat of severe storms. Based largely on WPC guidance, 0.5-1.0" of rain is generally expected. As mentioned above, forcing aloft is a little better late Tuesday, albeit with less instability (though forecast soundings do show some thin MUCAPE that may enhance parcel lift). The front isn`t expected to make much progress eastward, so there may be a limited flooding threat worth watching Tuesday evening, largely dependent on how active the front is tonight and Tuesday. Lows again in the upper 60s.
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&& .LONG TERM /WEDNESDAY THROUGH MONDAY/...
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As of 345 AM Monday... PoPs will be higher...chance category...in the east on Wednesday due to proximity of the lingering frontal zone where moisture advection will maintain precipitable waters in excess of 1.5 inches. Dry air wrapping into the area around the upper low will be sufficient to produce a chance of thunder...especially I95 eastward. Highs will be similar to Tuesday...mid-upper 70s with some lower 80s in the southeast. Upper cutoff low over the Great Lakes throws a lot of uncertainty into the forecast heading into the late week...but at this point both GFS and ECWMF stall the southerly and easterly progress of the system in the Tennessee Valley and lift it back north into the Great Lakes over the weekend. Dry trajectory and maintenance of neutral temperature advection around the low supports our ongoing dry and seasonable forecast with highs mostly in the mid to upper 80s. Morning lows will feel nippy...with mins falling into the mid to upper 50s.
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&& .AVIATION /19Z MONDAY THROUGH SATURDAY/... As of 140 PM Monday... Stratus is slowly eroding from south to north, leading to VFR at RWI AND FAY, and should yield VFR at RDU by 19Z and GSO/INT by around 21Z. Scattered shower and a few storms will move into the vicinity of GSO/INT this evening, with showers possible throughout the night as a slow moving cold front inches into NC from the west. Most, if not all of the showers will remain west of RDU. If winds are light enough, some MVFR or IFR vsbys are possible at FAY and RWI overnight, though confidence is low. The front and associated showers will continue to shift slowly east on Tuesday, focusing more in the vicinity of RDU by midday. MVFR or VFR conditions are expected to be predominate. Looking beyond the 24 TAF Period: The combination of the stalled front and an upper low over the Tennessee Valley will continue the unsettled weather Tuesday night and Wednesday. Conditions are expected to improve to VFR from northwest to southeast by Wednesday night as drier air filters into the area. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...BS NEAR TERM...BS SHORT TERM...BS LONG TERM...MLM AVIATION...BS

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